/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util;

import org.springframework.lang.Nullable;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.text.ParseException;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

/**
 * Miscellaneous utility methods for number conversion and parsing.
 * <p>Mainly for internal use within the framework; consider Apache's
 * Commons Lang for a more comprehensive suite of number utilities.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 1.1.2
 */
public abstract class NumberUtils
{

    /**
     * Standard number types (all immutable):
     * Byte, Short, Integer, Long, BigInteger, Float, Double, BigDecimal.
     */
    public static final  Set<Class<?>> STANDARD_NUMBER_TYPES;
    private static final BigInteger    LONG_MIN = BigInteger.valueOf(Long.MIN_VALUE);
    private static final BigInteger    LONG_MAX = BigInteger.valueOf(Long.MAX_VALUE);

    static
    {
        Set<Class<?>> numberTypes = new HashSet<>(8);
        numberTypes.add(Byte.class);
        numberTypes.add(Short.class);
        numberTypes.add(Integer.class);
        numberTypes.add(Long.class);
        numberTypes.add(BigInteger.class);
        numberTypes.add(Float.class);
        numberTypes.add(Double.class);
        numberTypes.add(BigDecimal.class);
        STANDARD_NUMBER_TYPES = Collections.unmodifiableSet(numberTypes);
    }


    /**
     * Convert the given number into an instance of the given target class.
     *
     * @param number      the number to convert
     * @param targetClass the target class to convert to
     * @return the converted number
     * @throws IllegalArgumentException if the target class is not supported
     *                                  (i.e. not a standard Number subclass as included in the JDK)
     * @see java.lang.Byte
     * @see java.lang.Short
     * @see java.lang.Integer
     * @see java.lang.Long
     * @see java.math.BigInteger
     * @see java.lang.Float
     * @see java.lang.Double
     * @see java.math.BigDecimal
     */
    @SuppressWarnings("unchecked")
    public static <T extends Number> T convertNumberToTargetClass(Number number, Class<T> targetClass) throws IllegalArgumentException
    {

        Assert.notNull(number, "Number must not be null");
        Assert.notNull(targetClass, "Target class must not be null");

        if (targetClass.isInstance(number))
        {
            return (T) number;
        }
        else if (Byte.class == targetClass)
        {
            long value = checkedLongValue(number, targetClass);
            if (value < Byte.MIN_VALUE || value > Byte.MAX_VALUE)
            {
                raiseOverflowException(number, targetClass);
            }
            return (T) Byte.valueOf(number.byteValue());
        }
        else if (Short.class == targetClass)
        {
            long value = checkedLongValue(number, targetClass);
            if (value < Short.MIN_VALUE || value > Short.MAX_VALUE)
            {
                raiseOverflowException(number, targetClass);
            }
            return (T) Short.valueOf(number.shortValue());
        }
        else if (Integer.class == targetClass)
        {
            long value = checkedLongValue(number, targetClass);
            if (value < Integer.MIN_VALUE || value > Integer.MAX_VALUE)
            {
                raiseOverflowException(number, targetClass);
            }
            return (T) Integer.valueOf(number.intValue());
        }
        else if (Long.class == targetClass)
        {
            long value = checkedLongValue(number, targetClass);
            return (T) Long.valueOf(value);
        }
        else if (BigInteger.class == targetClass)
        {
            if (number instanceof BigDecimal)
            {
                // do not lose precision - use BigDecimal's own conversion
                return (T) ((BigDecimal) number).toBigInteger();
            }
            else
            {
                // original value is not a Big* number - use standard long conversion
                return (T) BigInteger.valueOf(number.longValue());
            }
        }
        else if (Float.class == targetClass)
        {
            return (T) Float.valueOf(number.floatValue());
        }
        else if (Double.class == targetClass)
        {
            return (T) Double.valueOf(number.doubleValue());
        }
        else if (BigDecimal.class == targetClass)
        {
            // always use BigDecimal(String) here to avoid unpredictability of BigDecimal(double)
            // (see BigDecimal javadoc for details)
            return (T) new BigDecimal(number.toString());
        }
        else
        {
            throw new IllegalArgumentException("Could not convert number [" + number + "] of type [" + number.getClass()
                    .getName() + "] to unsupported target class [" + targetClass.getName() + "]");
        }
    }

    /**
     * Check for a {@code BigInteger}/{@code BigDecimal} long overflow
     * before returning the given number as a long value.
     *
     * @param number      the number to convert
     * @param targetClass the target class to convert to
     * @return the long value, if convertible without overflow
     * @throws IllegalArgumentException if there is an overflow
     * @see #raiseOverflowException
     */
    private static long checkedLongValue(Number number, Class<? extends Number> targetClass)
    {
        BigInteger bigInt = null;
        if (number instanceof BigInteger)
        {
            bigInt = (BigInteger) number;
        }
        else if (number instanceof BigDecimal)
        {
            bigInt = ((BigDecimal) number).toBigInteger();
        }
        // Effectively analogous to JDK 8's BigInteger.longValueExact()
        if (bigInt != null && (bigInt.compareTo(LONG_MIN) < 0 || bigInt.compareTo(LONG_MAX) > 0))
        {
            raiseOverflowException(number, targetClass);
        }
        return number.longValue();
    }

    /**
     * Raise an <em>overflow</em> exception for the given number and target class.
     *
     * @param number      the number we tried to convert
     * @param targetClass the target class we tried to convert to
     * @throws IllegalArgumentException if there is an overflow
     */
    private static void raiseOverflowException(Number number, Class<?> targetClass)
    {
        throw new IllegalArgumentException("Could not convert number [" + number + "] of type [" + number.getClass()
                .getName() + "] to target class [" + targetClass.getName() + "]: overflow");
    }

    /**
     * Parse the given {@code text} into a {@link Number} instance of the given
     * target class, using the corresponding {@code decode} / {@code valueOf} method.
     * <p>Trims all whitespace (leading, trailing, and in between characters) from
     * the input {@code String} before attempting to parse the number.
     * <p>Supports numbers in hex format (with leading "0x", "0X", or "#") as well.
     *
     * @param text        the text to convert
     * @param targetClass the target class to parse into
     * @return the parsed number
     * @throws IllegalArgumentException if the target class is not supported
     *                                  (i.e. not a standard Number subclass as included in the JDK)
     * @see Byte#decode
     * @see Short#decode
     * @see Integer#decode
     * @see Long#decode
     * @see #decodeBigInteger(String)
     * @see Float#valueOf
     * @see Double#valueOf
     * @see java.math.BigDecimal#BigDecimal(String)
     */
    @SuppressWarnings("unchecked")
    public static <T extends Number> T parseNumber(String text, Class<T> targetClass)
    {
        Assert.notNull(text, "Text must not be null");
        Assert.notNull(targetClass, "Target class must not be null");
        String trimmed = StringUtils.trimAllWhitespace(text);

        if (Byte.class == targetClass)
        {
            return (T) (isHexNumber(trimmed) ? Byte.decode(trimmed) : Byte.valueOf(trimmed));
        }
        else if (Short.class == targetClass)
        {
            return (T) (isHexNumber(trimmed) ? Short.decode(trimmed) : Short.valueOf(trimmed));
        }
        else if (Integer.class == targetClass)
        {
            return (T) (isHexNumber(trimmed) ? Integer.decode(trimmed) : Integer.valueOf(trimmed));
        }
        else if (Long.class == targetClass)
        {
            return (T) (isHexNumber(trimmed) ? Long.decode(trimmed) : Long.valueOf(trimmed));
        }
        else if (BigInteger.class == targetClass)
        {
            return (T) (isHexNumber(trimmed) ? decodeBigInteger(trimmed) : new BigInteger(trimmed));
        }
        else if (Float.class == targetClass)
        {
            return (T) Float.valueOf(trimmed);
        }
        else if (Double.class == targetClass)
        {
            return (T) Double.valueOf(trimmed);
        }
        else if (BigDecimal.class == targetClass || Number.class == targetClass)
        {
            return (T) new BigDecimal(trimmed);
        }
        else
        {
            throw new IllegalArgumentException("Cannot convert String [" + text + "] to target class [" + targetClass.getName() + "]");
        }
    }

    /**
     * Parse the given {@code text} into a {@link Number} instance of the
     * given target class, using the supplied {@link NumberFormat}.
     * <p>Trims the input {@code String} before attempting to parse the number.
     *
     * @param text         the text to convert
     * @param targetClass  the target class to parse into
     * @param numberFormat the {@code NumberFormat} to use for parsing (if
     *                     {@code null}, this method falls back to {@link #parseNumber(String, Class)})
     * @return the parsed number
     * @throws IllegalArgumentException if the target class is not supported
     *                                  (i.e. not a standard Number subclass as included in the JDK)
     * @see java.text.NumberFormat#parse
     * @see #convertNumberToTargetClass
     * @see #parseNumber(String, Class)
     */
    public static <T extends Number> T parseNumber(String text, Class<T> targetClass, @Nullable NumberFormat numberFormat)
    {

        if (numberFormat != null)
        {
            Assert.notNull(text, "Text must not be null");
            Assert.notNull(targetClass, "Target class must not be null");
            DecimalFormat decimalFormat   = null;
            boolean       resetBigDecimal = false;
            if (numberFormat instanceof DecimalFormat)
            {
                decimalFormat = (DecimalFormat) numberFormat;
                if (BigDecimal.class == targetClass && !decimalFormat.isParseBigDecimal())
                {
                    decimalFormat.setParseBigDecimal(true);
                    resetBigDecimal = true;
                }
            }
            try
            {
                Number number = numberFormat.parse(StringUtils.trimAllWhitespace(text));
                return convertNumberToTargetClass(number, targetClass);
            }
            catch (ParseException ex)
            {
                throw new IllegalArgumentException("Could not parse number: " + ex.getMessage());
            }
            finally
            {
                if (resetBigDecimal)
                {
                    decimalFormat.setParseBigDecimal(false);
                }
            }
        }
        else
        {
            return parseNumber(text, targetClass);
        }
    }

    /**
     * Determine whether the given {@code value} String indicates a hex number,
     * i.e. needs to be passed into {@code Integer.decode} instead of
     * {@code Integer.valueOf}, etc.
     */
    private static boolean isHexNumber(String value)
    {
        int index = (value.startsWith("-") ? 1 : 0);
        return (value.startsWith("0x", index) || value.startsWith("0X", index) || value.startsWith("#", index));
    }

    /**
     * Decode a {@link java.math.BigInteger} from the supplied {@link String} value.
     * <p>Supports decimal, hex, and octal notation.
     *
     * @see BigInteger#BigInteger(String, int)
     */
    private static BigInteger decodeBigInteger(String value)
    {
        int     radix    = 10;
        int     index    = 0;
        boolean negative = false;

        // Handle minus sign, if present.
        if (value.startsWith("-"))
        {
            negative = true;
            index++;
        }

        // Handle radix specifier, if present.
        if (value.startsWith("0x", index) || value.startsWith("0X", index))
        {
            index += 2;
            radix = 16;
        }
        else if (value.startsWith("#", index))
        {
            index++;
            radix = 16;
        }
        else if (value.startsWith("0", index) && value.length() > 1 + index)
        {
            index++;
            radix = 8;
        }

        BigInteger result = new BigInteger(value.substring(index), radix);
        return (negative ? result.negate() : result);
    }

}
